1. Cats with senility or dementia will do this; I think it reflects the confusion and/or anxiety that they are experiencing. Many of these cats will experience memory loss, possibly inappropriate elimination, staring off into space or acting like they don't quite know where they are at times. Signs can be intermittent but the condition does tend to progress.
Treatment options are limited, unfortunately.
a) Feliway diffusers or a spray which are natural pheromones which can sometimes instill a sense of calm may be helpful. There a similar oral product called Composure Chews. These products are available on the internet or at most pet stores
b) Fish oil supplements such as Welactin may help some cats because of their anti-oxidant properties. c). Specific cognitive supplements such as Neutricks, SAMe (Novifit) and Senilife may be useful as well as NuCat Senior supplement. All of these products should be available on the internet if they aren't found locally.
2. Cats with hyperthyroid disease will often excessively vocalize. I don't have a good explanation for this (probably secondary to hypertension....see below) but I see it all the time. Blood work would diagnose this problem and there are good treatments for this disease although I can understand your reluctance to have him seen and possibly treated.
3. Cats with arthritis pain or other pain in their bodies will vocalize. We are also somewhat limited in treating cats with this problem but options to consider would include:
a. Cosequin for Cats which is a joint supplement. b. Occasional use of anti-inflammatory drugs such as Onisor which is licensed for use in cats but can only be given for three days in a row. There is a drug called Metacam but it is somewhat controversial in veterinary medicine. It's use can cause significant damage to the kidneys and should be used with great caution in older cats.
c. Adequan which is basically a stronger supplement but is an injection and needs to be given by your vet. d. Fish oil supplements as I mentioned above e. Pain medication such as Buprenex can be very useful and could be given every day or only on the days that he needs it but, again, would have to be dispensed by your vet. You may already be aware that cats shouldn't be given over the counter medication since it can be harmful for them.
4. Cats with hypertension can behave in some odd ways. This is rarely a primary problem in cats but usually secondary to Hyperthyroid Disease (#2 above) or kidney issues. Blood work would help diagnose either one of these conditions.
And blood pressure measurements are routinely done in cats these days and they can be treated for it, similar to a human.
6. I always worry about a brain mass when older cats start to behave in odd ways. I only include this to be complete but not to alarm you.
I often suggest that owners give their cats over the counter, human Melatonin which can help some of them sleep at night and thus prevent the heart-stopping screaming. The dose would be 3-12mg about one hour or so before bedtime; I usually start with the lower dose. For some cats, it can take several weeks before improvement is seen. Nature's Bounty is a good manufacturer since what's in the bottle is not necessarily what's on the label.
I hope this helps and that at least one or more of my suggestions will help curtail this behavior. It really is quite unsettling! Deb